Particulate measurement apparatus and particulate measurement system

ABSTRACT

A particulate measurement apparatus controls a particulate sensor which includes an ion generation section (110), an exhaust gas electrification section (120), an ion trapping section (130), and a second electrode (132). The second electrode (132) is maintained at a potential repulses the ions to assist the trapping of the ions at the ion trapping section (130). The particulate measurement apparatus includes a second isolation transformer (720b) and an auxiliary electrode current measurement circuit (780). The second isolation transformer (720b) applies a voltage to the second electrode (132) through a second wiring line (222). The auxiliary electrode current measurement circuit (780) detects an auxiliary electrode current Iir flowing to the second wiring line (222). The particulate measurement apparatus determines at least one of the state of the particulate sensor and the state of the second wiring line (222) based on the auxiliary electrode current Iir.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a particulate measurement apparatus and system which measure the amount of particulates such as soot contained in a gas under measurement.

2. Description of the Related Art

Conventionally, a particulate measurement system has been known which measures the amount of particulates (e.g., soot) contained in a gas under measurement (for example, exhaust gas discharged from an internal combustion engine or the like) (see, for example, Patent Document 1).

Such a particulate measurement system includes a particulate sensor which is exposed to the gas under measurement and detects particulates. The particulate sensor includes an ion generation section, an electrification chamber, a trapping section, and an auxiliary electrode section.

The particulate measurement system electrifies at least a portion of particulates contained in the gas under measurement in the electrification chamber using ions generated at the ion generation section by means of corona discharge, and measures the amount of particulates based on the amount of ions trapped by the trapping section. Notably, the auxiliary electrode section is maintained at a potential which repulse the ions to thereby assist the trapping of ions at the trapping section.

[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2013-195069

3. Problems to be Solved by the Invention

However, a problem arises in the particulate measurement system described above in that when particulates (soot, etc.) adhere to the particulate sensor, the accuracy in measuring the amount of particulates is lowered or measurement of the amount of particulates can no longer be carried out.

For example, when the insulation resistance between the auxiliary electrode section and the reference potential (ground potential) decreases due to particulates, etc., having adhered to the particulate sensor, an irregular current may flow through the adhered particulates, etc. Also, an irregular current may flow when a voltage application path for applying a voltage to the auxiliary electrode section suffers an electrical anomaly (for example, a short circuit between the voltage application path and the ground). If such an irregular current flows, the amount of ions trapped by the trapping section is in error, which adversely affects the measurement of the amount of particulates.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to suppress lowering of the measurement performance of the particulate sensor.

The above object has been achieved by providing (1) a particulate measurement apparatus for controlling a particulate sensor which measures the amount of particulates contained in a gas under measurement and which comprises an ion generation section, an electrification chamber, a trapping section, and an auxiliary electrode section including an auxiliary electrode. The ion generation section generates ions by means of corona discharge. The electrification chamber electrifies at least a portion of the particulates contained in a gas under measurement by using the ions generated in the ion generation section. The trapping section traps at least a portion of the ions generated by the ion generation section but not used for electrifying the particulates. The auxiliary electrode section is maintained at a potential which repulses the unused ions and which assists in the trapping of the unused ions at the trapping section.

The particulate measurement apparatus of the present invention comprises a voltage application section, a current detection section, and a state determination section. The voltage application section applies a voltage to the auxiliary electrode through a voltage application path, the applied voltage assisting the trapping of the ions at the trapping section. The current detection section detects auxiliary electrode current flowing to the voltage application path. The state determination section determines at least one of a state of the particulate sensor and a state of the voltage application path based on the auxiliary electrode current detected by the current detection section.

Notably, the above-described voltage application path refers to a portion (for example, a conductor wire connecting the voltage application section and the auxiliary electrode) whose voltage becomes equal to the output voltage from the voltage application section when the output voltage from the voltage application section is applied thereto.

The particulate measurement apparatus of the present invention configured as described above can determine that at least one of the particulate sensor and the voltage application path is in a state which is not normal, by detecting the auxiliary electrode current which does not flow when the particulate sensor is in a normal operating state.

In a state in which the auxiliary electrode current flows, the measurement performance of the particulate sensor may be lowered. In contrast, since the particulate measurement apparatus of the present invention can determine the state in which the auxiliary electrode current is flowing, the particulate measurement apparatus can prevent the particulate sensor from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current. Thus, the particulate measurement apparatus of the present invention can suppress a lowering of the measurement performance of the particulate sensor.

In a preferred embodiment (2) of the particulate measurement apparatus (1), the state determination section determines the state of the particulate sensor by comparing the auxiliary electrode current and a state judgment value set in advance based on a relation between the state of the particulate sensor and the auxiliary electrode current.

The particulate measurement apparatus configured as described above can determine the state of the particulate sensor by a simple method of comparing the auxiliary electrode current and the state judgment value. Therefore, the processing load of the particulate measurement apparatus can be reduced.

In another preferred embodiment (3) of the particulate measurement apparatus (2) above, a plurality of state judgment values is set in advance, and the state determination section determines, as the state of the particulate sensor, one of states set in advance to differ from one another and which correspond to the plurality of state judgment values, based on the results of comparison between the plurality of state judgment values and the auxiliary electrode current.

The particulate measurement apparatus configured as described above can determine a plurality of states of the particulate sensor which differ from one another based on the auxiliary electrode current. Therefore, the particulate measurement apparatus of the present invention can properly perform the processing of suppressing a lowering of the measurement performance of the particulate sensor in accordance with the auxiliary electrode current.

In yet another preferred embodiment (4), the particulate measurement apparatus of any of (1) to (3) above further comprises a suppression processing execution section which executes suppression processing for suppressing a lowering of measurement performance of the particulate sensor in accordance with the result of the determination by the state determination section. In this case, the particulate measurement apparatus of the present invention can perform proper processing in accordance with the state of the particulate sensor so as to suppress the lowering of the measurement performance of the particulate sensor.

In yet another preferred embodiment (5) of the particulate measurement apparatus (4) above, the suppression processing comprises processing of annunciating the result of the determination by the state determination section.

The particulate measurement apparatus of the present invention configured as described above can prompt a user of the particulate measurement apparatus to exchange the particulate sensor or to perform a process of removing particulates having adhered to the particulate sensor, by annunciating the result of the determination by the state determination section. Therefore, the particulate measurement apparatus of the present invention can prevent the particulate sensor from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current. Thus, the particulate measurement apparatus of the present invention can suppress a lowering of the measurement performance of the particulate sensor.

In yet another preferred embodiment (6) of the particulate measurement apparatus (4) above, the particulate sensor includes an auxiliary electrode heating section which is disposed around the auxiliary electrode section and which heats the auxiliary electrode section when the auxiliary electrode heating section is energized, and the suppression processing comprises processing of supplying electric current to the auxiliary electrode heating section.

The particulate measurement apparatus of the present invention configured as described above can remove particulates adhering to the vicinity of the auxiliary electrode by supplying electric current to the auxiliary electrode heating section, to thereby return the particular sensor to a state in which the auxiliary electrode current does not flow. Therefore, the particulate measurement apparatus of the present invention can prevent the particulate sensor from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current. Thus, the particulate measurement apparatus of the present invention can suppress a lowering of the measurement performance of the particulate sensor.

In a second aspect (7), the present invention provides a particulate measurement system comprising a particulate measurement apparatus of any of (1) to (6) above; and a particulate sensor connected to the particulate measurement apparatus. Therefore, the particulate measurement system of the present invention can determine that the particulate sensor is in a state which is not normal by detecting the auxiliary electrode current which does not flow when the particulate sensor operates normally. Thus, the particulate measurement system of the present invention can suppress a lowering of the measurement performance of the particulate sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are explanatory views of an overall configuration of a particulate measurement system.

FIG. 2 is an explanatory view schematically showing the structure of a distal end portion of a particulate sensor.

FIG. 3 is a block diagram schematically exemplifying the configuration of an electric circuit section.

FIG. 4 is a circuit diagram schematically exemplifying the configuration of an ion current measurement circuit.

FIG. 5 is a circuit diagram schematically exemplifying the configuration of a corona current measurement circuit.

FIG. 6 is a circuit diagram schematically exemplifying the configuration of an auxiliary electrode current measurement circuit.

FIG. 7 is a flowchart showing sensor state determination processing of a first embodiment.

FIG. 8 is a flowchart showing sensor state determination processing of a second embodiment.

FIG. 9 is a block diagram schematically exemplifying the configuration of an electric circuit section of a third embodiment.

FIG. 10 is a flowchart showing particulate removal processing.

DESCRIPTION OF REFERENCE NUMERALS

Reference numerals used to identify various features in the drawings include the following.

10 . . . particulate measurement system, 100 . . . particulate sensor, 110 . . . ion generation section, 120 . . . exhaust gas electrification section, 130 . . . ion trapping section, 132 . . . second electrode, 140 . . . auxiliary electrode heating section, 222 . . . second wiring line, 300 . . . particulate measurement apparatus, 600 . . . control section, 700 . . . electric circuit section, 710 . . . power supply circuit, 710 b . . . second power supply circuit, 711 b . . . second discharge voltage control circuit, 712 b . . . second transformer drive circuit, 720 . . . isolation transformer, 720 b . . . second isolation transformer, 780 . . . auxiliary electrode current measurement circuit, 790 . . . heater energization circuit

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will next be described in greater detail with reference to the drawings. However, the present invention should not be construed as being limited thereto.

1. First Embodiment

1-1. Overall Configuration

The configuration of a particulate measurement system according to a first embodiment will next be described.

FIGS. 1A and 1B are explanatory views used of an overall configuration of a particulate measurement system 10 according to the first embodiment. FIG. 1A is an explanatory view schematically exemplifying the structure of a vehicle 500 on which the particulate measurement system 10 is mounted. FIG. 1B is an explanatory view schematically exemplifying the configuration of the particulate measurement system 10 attached to the vehicle 500.

The particulate measurement system 10 includes a particulate sensor 100, a cable 200, and a particulate measurement apparatus 300, and measures the amount of particulates such as soot contained in exhaust gas discharged from an internal combustion engine 400. The internal combustion engine 400, which is a power source of the vehicle 500, is a diesel engine or the like.

The particulate sensor 100 is attached to an exhaust gas pipe 402 extending from the internal combustion engine 400, and is electrically connected to the particulate measurement apparatus 300 through the cable 200. In the present embodiment, the particulate sensor 100 is attached to a portion of the exhaust gas pipe 402, which portion is located downstream of a filter apparatus 410 (for example, a DPF (diesel particulate filter)). The particulate sensor 100 outputs to the particulate measurement apparatus 300 a signal which correlates with the amount of particulates contained in the exhaust gas.

The particulate measurement apparatus 300 drives the particulate sensor 100 and detects (measures) the amount of particulates contained in the exhaust gas based on the signal supplied from the particulate sensor 100. The “amount of particulates contained in the exhaust gas” detected by the particulate measurement apparatus 300 may be a value which is proportional to the sum of the surface areas of particulates contained in the exhaust gas or a value which is proportional to the sum of the masses of the particulates. Alternatively, the amount of particulates contained in the exhaust gas may be a value which is proportional to the number of particulates contained in a unit volume of the exhaust gas.

A vehicle control section 420 controls the combustion state of the internal combustion engine 400, the amount of fuel supplied from a fuel supply section 430 to the internal combustion engine 400 through a fuel pipe 405, etc. The particulate measurement apparatus 300 and the vehicle control section 420 are electrically connected to a power supply section 440, and electric power is supplied from the power supply section 440 to the particulate measurement apparatus 300 and the vehicle control section 420.

As shown in FIG. 1B, the particulate sensor 100 has a cylindrical distal end portion 100 e, and is fixed to the outer surface of the exhaust gas pipe 402 such that the distal end portion 100 e is inserted into the exhaust gas pipe 402. In the present embodiment, the distal end portion 100 e of the particulate sensor 100 is inserted approximately perpendicular to an extension direction DL of the exhaust gas pipe 402. A casing CS of the distal end portion 100 e has an inflow hole 45 and a discharge hole 35 formed on the surface of the casing CS. The inflow hole 45 is used to introduce the exhaust gas into the interior of the casing CS, and the discharge hole 35 is used to discharge the introduced exhaust gas to the outside of the casing CS. A portion of the exhaust gas F flowing through the exhaust gas pipe 402 is introduced into the interior of the casing CS of the distal end portion 100 e through the inflow hole 45. Particulates contained in the introduced exhaust gas are electrified by ions (positive ions in the present embodiment) generated by the particulate sensor 100. The exhaust gas containing the electrified particulates is discharged to the outside of the casing CS through the discharge hole 35. The internal structure of the casing CS and the specific structure of the particulate sensor 100 will be described below.

The cable 200 is attached to a rear end portion 100 r of the particulate sensor 100. The cable 200 includes a first wiring line 221, a second wiring line 222, a signal line 223, and an air supply tube 224 bundled together. Each of the wiring lines 221 to 223 and the air supply tube 224, which constitute the cable 200, is formed of a flexible member. The first wiring line 221, the second wiring line 222, and the signal line 223 are electrically connected to an electric circuit section 700 of the particulate measurement apparatus 300, and the air supply tube 224 is connected to an air supply section 800 of the particulate measurement apparatus 300.

The particulate measurement apparatus 300 includes a control section 600, the electric circuit section 700, the air supply section 800, a housing 910, a display section 920, and an operation input section 930.

The housing 910 is formed into a box-like shape, and accommodates the control section 600, the electric circuit section 700, the air supply section 800, the display section 920, and the operation input section 930. Notably, the housing 910 is configured to allow a user to carry the particulate measurement apparatus 300. The particulate measurement apparatus 300 is carried to a location where the user wants to attach the particulate sensor 100 to a vehicle, and the particulate measurement apparatus 300 is mounted on the vehicle for use.

The display section 920 includes a display unit attached to the housing 910, which displays various images on the display screen of the display unit.

The operation input section 930 includes switches attached to the housing 910, and outputs input operation information for specifying an input operation performed by the user through use of the switches.

The control section 600 includes a microcomputer, executes various types of processing based on inputs from the electric circuit section 700 and the operation input section 930, and controls the electric circuit section 700, the air supply section 800, and the display section 920. Also, the control section 600 detects (measures) the amount of particulates contained in the exhaust gas based on a signal supplied from the electric circuit section 700.

The electric circuit section 700 supplies electric power to the particulate sensor 100 through the first wiring line 221 and the second wiring line 222 so as to drive the particulate sensor 100. A signal which correlates with the amount of particulates contained in the exhaust gas is supplied from the particulate sensor 100 to the electric circuit section 700 through the signal line 223. Using this signal supplied through the signal line 223, the electric circuit section 700 outputs to the control section 600 a signal corresponding to the amount of particulates contained in the exhaust gas. These signals will be described in detail below.

The air supply section 800 includes a pump (not shown), and supplies high-pressure air to the particulate sensor 100 through the air supply tube 224 in response to an instruction from the control section 600. The high-pressure air supplied from the air supply section 800 is used to drive the particulate sensor 100. Notably, instead of supplying air from the air supply section 800, another type of gas may be supplied to the particulate sensor 100.

1-2. Particulate Sensor

FIG. 2 is an explanatory view schematically showing the structure of the distal end portion 100 e of the particulate sensor 100.

The distal end portion 100 e of the particulate sensor 100 includes an ion generation section 110, an exhaust gas electrification section 120, and an ion trapping section 130. The casing CS has a structure in which the three mechanism sections; i.e., the ion generation section 110, the exhaust gas electrification section 120, and the ion trapping section 130, are arranged in this order from the proximal end side (the upper side in FIG. 2) of the distal end portion 100 e toward the distal end side (the lower side in FIG. 2) thereof (along the axial direction of the particulate sensor 100). The casing CS is formed of an electrically conductive material, and is connected to a secondary-side ground SGL (FIG. 3) through the signal line 223 (FIG. 1B).

The ion generation section 110 is a mechanism which generates ions (positive ions in the present embodiment) which are supplied to the exhaust gas electrification section 120. The ion generation section 110 includes an ion generation chamber 111 and a first electrode 112. The ion generation chamber 111 is a small space formed inside the casing CS. An air supply hole 55 and a nozzle 41 are provided on the inner circumferential surface of the ion generation chamber 111. The first electrode 112 is attached such that it projects into the ion generation chamber 111. The air supply hole 55 communicates with the air supply tube 224 (FIG. 1B), and the high-pressure air supplied from the air supply section 800 (FIG. 1B) is supplied to the ion generation chamber 111 through the air supply hole 55. The nozzle 41 is a very small hole (orifice) provided near the center of a partition wall 42 between the ion generation section 110 and the exhaust gas electrification section 120. The nozzle 41 supplies the ions generated in the ion generation chamber 111 to an electrification chamber 121 of the exhaust gas electrification section 120. The first electrode 112 has a rod-like outer shape, and its base end portion is fixed to the casing CS via a ceramic pipe 25 in a state in which a distal end portion of the first electrode 112 is located near the partition wall 42. The first electrode 112 is connected to the electric circuit section 700 (FIG. 1B) through the first wiring line 221 (FIG. 1B).

The ion generation section 110 is configured such that, using the electric power supplied from the electric circuit section 700, a voltage (e.g., 2 to 3 kV) is applied between the first electrode 112 (positive pole) and the partition wall 42 (negative pole). As a result, the ion generation section 110 produces a corona discharge between a distal end portion of the first electrode 112 and the partition wall 42 to thereby generate positive ions PI. The positive ions PI generated in the ion generation section 110 are jetted into the electrification chamber 121 of the exhaust gas electrification section 120 through the nozzle 41 together with the high-pressure air supplied from the air supply section 800 (FIG. 1B). The jetting speed of air jetted from the nozzle 41 may be set to a speed near the speed of sound.

The exhaust gas electrification section 120 electrifies the particulates contained in the exhaust gas by positive ions PI, and includes the above-mentioned electrification chamber 121. The electrification chamber 121 is a small space located adjacent to the ion generation chamber 111, and communicates with the ion generation chamber 111 through the nozzle 41. Also, the electrification chamber 121 communicates with the outside of the casing CS through the inflow hole 45, and communicates with a trapping chamber 131 of the ion trapping section 130 through a gas flow passage 31. The electrification chamber 121 is configured such that, when air containing the positive ions PI are jetted from the nozzle 41, a negative pressure is created in the electrification chamber 121, and the exhaust gas located outside the casing CS flows into the electrification chamber 121 through the inflow hole 45. Therefore, the air jetted from the nozzle 41 and containing the positive ions PI and the exhaust gas flowing inward through the inflow hole 45 are mixed together within the electrification chamber 121. At that time, at least a portion of the soot S (particulates) contained in the exhaust gas that has flowed inward through the inflow hole 45 is electrified by the positive ions PI supplied from the nozzle 41. The air containing the electrified soot S and the unused positive ions PI is supplied to the trapping chamber 131 of the ion trapping section 130 through the gas flow passage 31.

The ion trapping section 130 traps ions not used for electrifying the soot S (particulates), and includes the above-mentioned trapping chamber 131 and a second electrode 132. The trapping chamber 131 is a small space located adjacent to the electrification chamber 121, and communicates with the electrification chamber 121 through the gas flow passage 31. Also, the trapping chamber 131 communicates with the outside of the casing CS through the discharge hole 35. The second electrode 132 has a generally rod-like outer shape and is fixed to the casing CS such that its longitudinal direction coincides with the flow direction of air flowing through the gas flow passage 31 (the extending direction of the casing CS). The second electrode 132 is connected to the electric circuit section 700 (FIG. 1B) through the second wiring line 222 (FIG. 1B). The second electrode 132 is electrically insulated from the casing CS.

A voltage of about 100 V is applied to the second electrode 132, whereby it functions as an auxiliary electrode for trapping positive ions not used for electrifying the soot S. Specifically, using the electric power supplied from the electric circuit section 700, a voltage is applied to the ion trapping section 130 such that the second electrode 132 serves as a positive pole, and the casing CS constituting the electrification chamber 121 and the trapping chamber 131 serves as a negative pole. As a result, the positive ions PI not used for electrifying the soot S are repulsed by the second electrode 132, whereby the advancing directions of the positive ions PI deviate to directions away from the second electrode 132. The deviated positive ions PI are trapped by the inner circumferential walls of the trapping chamber 131 and the gas flow passage 31 which function as a negative pole. Meanwhile, the soot S to which positive ions PI have adhered are also repulsed by the second electrode 132 as in the case of the positive ions PI. However, since the soot S particulates are larger in mass than the positive ions PI, the influence of the repulsive force on the advancing directions of the electrified soot S is small as compared with the case of the positive ions PI. Therefore, the electrified soot S is discharged to the outside of the casing CS through the discharge hole 35 as a result of the flow of the exhaust gas.

The particulate sensor 100 outputs a signal indicating a change in current which corresponds to the amount of positive ions PI trapped in the ion trapping section 130. The control section 600 (FIG. 1B) detects the amount of soot S contained in the exhaust gas based on the signal output from the particulate sensor 100. A method of calculating the amount of soot S contained in the exhaust gas based on the signal output from the particulate sensor 100 will be described below.

1-3. Electric Circuit Section

FIG. 3 is a block diagram schematically exemplifying the configuration of the electric circuit section 700.

The electric circuit section 700 includes a power supply circuit 710, an isolation transformer 720, a corona current measurement circuit 730, an ion current measurement circuit 740, a first rectification circuit 751, a second rectification circuit 752, and an auxiliary electrode current measurement circuit 780.

The power supply circuit 710 includes a first power supply circuit 710 a and a second power supply circuit 710 b. The isolation transformer 720 includes a first isolation transformer 720 a and a second isolation transformer 720 b.

The first power supply circuit 710 a steps up the voltage (electric power) supplied from the power supply section 440, supplies the stepped up voltage to the first isolation transformer 720 a, and drives the first isolation transformer 720 a. The first power supply circuit 710 a includes a first discharge voltage control circuit 711 a and a first transformer drive circuit 712 a. Under the control by the control section 600, the first discharge voltage control circuit 711 a can arbitrarily change the voltage of the electric power supplied to the first isolation transformer 720 a. In the present embodiment, the control section 600 controls the voltage of the electric power supplied to the first isolation transformer 720 a such that an input current I_(in) supplied to the first electrode 112 of the particulate sensor 100 through the first wiring line 221 becomes equal to a target current I_(ta) (e.g., 5 μA) set in advance. The method of this control will be described below. As a result, the amount of positive ions PI generated by the corona discharge in the ion generation section 110 can be made constant.

The first transformer drive circuit 712 a includes a switch which can switch the flow direction of current flowing through the primary-side coil of the first isolation transformer 720 a. The first transformer drive circuit 712 a drives the first isolation transformer 720 a by the switching operation of the switch. In the present embodiment, the circuit type of the first isolation transformer 720 a is a push-pull type. However, the circuit type of the first isolation transformer 720 a is not limited thereto and may be, for example, a half-bridge type or a full-bridge type.

The first isolation transformer 720 a performs voltage conversion for the electric power supplied from the first power supply circuit 710 a, and supplies the voltage-converted electric power to the first rectification circuit 751 on the secondary side. The first isolation transformer 720 a of the present embodiment is configured such that the primary-side coil and the secondary-side coil are not in physical contact with each other but are magnetically coupled with each other. A circuit on the primary side of the first isolation transformer 720 a includes the control section 600 and the power supply section 440 as well as the first power supply circuit 710 a. A circuit on the secondary side of the first isolation transformer 720 a includes the particulate sensor 100 and the first rectification circuit 751.

The second power supply circuit 710 b steps up the voltage of electric power (DC electric power in the present embodiment) supplied from the power supply section 440, supplies the stepped up voltage to the second isolation transformer 720 b, and drives the second isolation transformer 720 b. The second power supply circuit 710 b includes a second discharge voltage control circuit 711 b and a second transformer drive circuit 712 b. Under the control by the control section 600, the second discharge voltage control circuit 711 b can arbitrarily change the voltage of the electric power supplied to the second isolation transformer 720 b. In the present embodiment, the control section 600 controls the voltage of the electric power supplied to the second isolation transformer 720 b such that the voltage supplied to the second electrode 132 of the particulate sensor 100 through the second wiring line 222 becomes equal to a target voltage (e.g., 100 V) set in advance.

The second transformer drive circuit 712 b includes a switch which can switch the flow direction of current flowing through the primary-side coil of the second isolation transformer 720 b. The second transformer drive circuit 712 b drives the second isolation transformer 720 b by the switching operation of the switch. In the present embodiment, the circuit type of the second isolation transformer 720 b is a push-pull type. However, the circuit type of the second isolation transformer 720 b is not limited thereto and may be, for example, a half-bridge type or a full-bridge type.

The second isolation transformer 720 b performs voltage conversion for the electric power supplied from the second power supply circuit 710 b, and supplies the voltage-converted electric power to the second rectification circuit 752 on the secondary side. The second isolation transformer 720 b of the present embodiment is configured such that the primary-side coil and the secondary-side coil are not in physical contact with each other but are magnetically coupled with each other. A circuit on the primary side of the second isolation transformer 720 b includes the control section 600 and the power supply section 440 as well as the second power supply circuit 710 b. A circuit on the secondary side of the second isolation transformer 720 b includes the particulate sensor 100 and the second rectification circuit 752.

The corona current measurement circuit 730, the ion current measurement circuit 740, and the auxiliary electrode current measurement circuit 780 are provided between the circuit on the primary side of the isolation transformer 720 (the first isolation transformer 720 a and the second isolation transformer 720 b) and the circuit on the secondary side of the isolation transformer 720 (the first isolation transformer 720 a and the second isolation transformer 720 b), and are electrically connected to the primary-side and secondary-side circuits, respectively. As described below, the corona current measurement circuit 730 is configured such that a circuit portion electrically connected to the circuit on the primary side of the isolation transformer 720 (the first isolation transformer 720 a and the second isolation transformer 720 b) is physically insulated from a circuit portion electrically connected to the circuit on the secondary side of the isolation transformer 720 (the first isolation transformer 720 a and the second isolation transformer 720 b). Here, a ground (ground wiring) which has the reference potential of the primary-side circuit is also referred to as a “primary-side ground PGL,” and a ground which has the reference potential of the secondary-side circuit is also referred to as a “secondary-side ground SGL.”

Ends of the primary-side coils of the isolation transformer 720 (the first isolation transformer 720 a and the second isolation transformer 720 b) are connected to the primary-side ground PGL, and ends of the secondary-side coils thereof are connected to the secondary-side ground SGL. One end of the signal line 223 is connected to the casing CS, and the other end of the signal line 223 is connected to the secondary-side ground SGL.

The first rectification circuit 751 is connected to the first electrode 112 through a short protection resistor 753, and supplies the converted electric power to the first electrode 112 through the first wiring line 221. Namely, the voltage supplied from the first rectification circuit 751 becomes mostly a discharge voltage at the first electrode 112, and the current supplied from the first rectification circuit 751 becomes an input current I_(in) input to the first electrode 112. The second rectification circuit 752 is connected to the second electrode 132 through a short protection resistor 754, and applies the converted voltage to the second electrode 132 through the second wiring line 222.

The ion current measurement circuit 740 detects a current (I_(esc)) corresponding to the positive ions PI having flowed out without being trapped by the ion trapping section 130 and supplies to the secondary-side circuit a current (compensation current I_(c)) corresponding to the positive ions PI having flowed out. The ion current measurement circuit 740 is connected to the signal line 223 on the secondary side (specifically, a portion of the signal line 223 located on the ion current measurement circuit 740 side with respect to the shunt resistor 230) through a wiring line 771, and is connected to the control section 600 on the primary side through wiring lines 772 and 773. Also, the ion current measurement circuit 740 is connected to the primary-side ground PGL through the wiring line 775. Through the wiring line 772, the ion current measurement circuit 740 outputs to the control section 600 a signal SW_(esc) showing a current corresponding to the amount of positive ions PI having flowed out without having been trapped by the ion trapping section 130. The ion current measurement circuit 740 also outputs a signal SS_(esc) to the control section 600 through the wiring line 773, the signal SS_(esc) being obtained by amplifying the signal SW_(esc) and serving as a high sensitivity signal.

The corona current measurement circuit 730 is connected to the signal line 223 through wiring lines 761 and 762, and is connected to the control section 600 through a wiring line 763. The wiring lines 761 and 762 are connected to the signal line 223 such that the shunt resistor 230 provided in the signal line 223 is located between the wiring lines 761 and 762. The corona current measurement circuit 730 outputs to the control section 600 a signal S_(dc+trp+c) representing a secondary-side current (I_(dc)+I_(trp)+I_(c)) flowing from the casing CS toward the secondary-side ground SGL through the signal line 223. Here, a “signal representing a current” is not limited to a signal which directly represents the current, and may be a signal which indirectly represents the current. For example, the “signal representing a current” may be a signal on the basis of which the current can be specified by applying a computation expression or a map to information obtained from the signal. Notably, since the compensation current I_(c) supplied (supplemented) from the ion current measurement circuit 740 corresponds to the current corresponding to the positive ions PI having flowed out of the casing CS, the secondary-side current which includes the compensation current I_(c) and which flows from the casing CS to the secondary-side ground SGL; i.e., the secondary-side current (I_(dc)+I_(trp)+I_(c)) flowing through the shunt resistor 230, becomes equal to the input current I_(in).

Using the signal S_(dc+trp+c) supplied from the corona current measurement circuit 730, the control section 600 controls the first discharge voltage control circuit 711 a such that the input current I_(in) becomes equal to the target current I_(ta). Namely, the corona current measurement circuit 730 and the control section 600 constitute a constant current circuit for maintaining the corona current (=the input current I_(in)) at a constant level. Since the corona current correlates with the amount of positive ions PI generated at the ion generation section 110, the amount of positive ions PI generated at the ion generation section 110 is maintained constant by this constant current circuit.

Next, a method will be described by which the ion current measurement circuit 740 detects the current corresponding to the positive ions PI having flowed out without having been trapped by the ion trapping section 130.

Here, the current supplied from the first wiring line 221 to the first electrode 112 is referred to as the “input current Iin”; the current flowing from the first electrode 112 to the casing CS through the partition wall 42 due to corona discharge is referred to as the “discharge current I_(dc)”; the current corresponding to the charge of the positive ions PI which are some of the positive ions PI generated due to corona discharge, are used for electrification of the soot S, and leak to the outside of the casing CS will be referred to as the “leakage current I_(esc)”; and the current corresponding to the charge of the positive ions PI trapped by the casing CS is referred to as the “trapped current I_(trp).” These four currents satisfy the relation of the following expression (1). I _(in) =I _(dc) +I _(trp) +I _(esc)   (1)

The leakage current I_(esc) is a signal which is output from the ion current measurement circuit 740 and which represents a current value corresponding to the current (the compensation current I_(c)) corresponding to the positive ions PI that have flowed out. Therefore, by detecting this compensation current I_(c) the ion current measurement circuit 740 can detect the current (I_(esp)) corresponding to the positive ions PI having flowed out without being trapped by the ion trapping section 130. Notably, the compensation current I_(c) is also a signal representing the difference between the primary-side ground PGL and the secondary-side ground PGL.

The auxiliary electrode current measurement circuit 780 is connected to the second wiring line 222 through wiring lines 781 and 782, and is connected to the control section 600 through a wiring line 783. The wiring line 781 and the wiring line 782 are connected to the second wiring line 222 such that the short protection resistor 754 provided in the second wiring line 222 is located between the wiring lines 781 and 782. The short protection resistor 754 functions as a resistor for short circuit protection when a short circuit is formed, and also functions as a shunt resistor for current detection.

The auxiliary electrode current measurement circuit 780 outputs to the control section 600 an auxiliary electrode current signal S_(ir) representing the auxiliary electrode current I_(ir) flowing to the second wiring line 222. When the particulate sensor 100 is operating normally, no current flows to the second wiring line 222 because the second electrode 132 and the casing CS are electrically insulated from each other. However, for example, when the second electrode 132 and the casing CS are electrically connected to each other (i.e., a short circuit is formed therebetween) by soot or the like, the auxiliary electrode current I_(ir) may flow to the second wiring line 222. Here, a “signal representing a current” is not limited to a signal which directly represents the current, and may be a signal which indirectly represents the current. For example, the “signal representing a current” may be a signal wherein the current is specified by applying a computation expression or a map to information obtained from the signal.

1-4. Ion Current Measuring System

FIG. 4 is an explanatory view schematically exemplifying the configuration of the ion current measurement circuit 740.

The ion current measurement circuit 740 includes a first operational amplifier AMP1, a second operational amplifier AMP2, a third operational amplifier AMPS, and resistors RE1 to RE5 having known resistances.

One input terminal of the first operational amplifier AMP1 is connected to the secondary-side ground SGL through the wiring line 771 and the signal line 223 (including the shunt resistor 230), and the other input terminal of the first operational amplifier AMP1 is connected to the primary-side ground PGL through the wiring line 775. The output terminal of the first operational amplifier AMP1 is connected to the control section 600 through the wiring line 772. Also, the output terminal of the first operational amplifier AMP1 is connected to one input terminal of the second operational amplifier AMP2 through a portion of the wiring line 772 and a wiring line LI1 and is connect to the wiring line 771 through a portion of the wiring line 772 and a wiring line LI2. The resistor RE1 is provided in the wiring line LI1 and the resistor RE2 is provided in the wiring line LI2.

One input terminal of the second operational amplifier AMP2 is connected to the first operational amplifier AMP1 through a portion of the wiring line LI1 and the wiring line 772, and the other input terminal of the second operational amplifier AMP2 is connected to the primary-side ground PGL through a wiring line LI3 and the wiring line 775. The resistor RE3 and the third operational amplifier AMP3 are provided in the wiring line LI3. A wiring line LI4 is connected to the wiring line LI3 at a position between the resistor RE3 and the third operational amplifier AMP3. The wiring line LI3 is connected to the wiring line LI1 through the wiring line LI4 in which the resistor RE4 is provided. The third operational amplifier AMP3 forms a voltage follower which suppresses voltage change due to current change on the output side. The output terminal of the second operational amplifier AMP2 is connected to the control section 600 through the wiring line 773, and is connected to the wiring line LI3 through the wiring line 773 and a wiring line LI5. The resistor RE5 is provided in the wiring line LI5.

When the leakage current I_(esc) is generated, the reference potential of the secondary-side ground SGL becomes lower than the reference potential of the primary-side ground PGL in accordance with the magnitude of the leakage current I_(esc). This is because a difference in energy corresponding to the leakage current I_(esc) is produced between the energy (electric power) supplied from the primary-side circuit (including the power supply circuit 710) to the particulate sensor 100 and the energy (electric power) output from the particulate sensor 100 through the signal line 223. When a difference is produced between the reference potential of the secondary-side ground SGL and the reference potential of the primary-side ground PGL as a result of generation of the leakage current I_(esc), the first operational amplifier AMP1 outputs a voltage corresponding to this difference. Since the voltage output from the first operational amplifier AMP1 correlates with the leakage current I_(esc), this voltage is output to the control section 600 through the wiring line 772 as a signal SW_(esc) representing the leakage current I_(esc).

Also, the voltage output from the first operational amplifier AMP1 produces the compensation current I_(c), which is supplied from the wiring line LI2 to the wiring line 771 through the resistor RE2. As described above, the compensation current I_(c) is equal to the leakage current I_(esc). Therefore, as a result of supply of the compensation current I_(c) to the wiring line 771 which constitutes the secondary-side circuit, the difference between the reference potential of the secondary-side ground SGL and the reference potential of the primary-side ground PGL is compensated.

The second operational amplifier AMP2 amplifies the signal SW_(esc) input from the first operational amplifier AMP1, and outputs to the control section 600 the signal SS_(esc) obtained as a result of the amplification. Since the second operational amplifier AMP2 forms a differential amplification circuit, the second operational amplifier AMP2 outputs a voltage corresponding to the difference between the voltage input to one input terminal as the signal SW_(esc) and the reference potential of the primary-side ground PGL input to the other input terminal. Namely, the second operational amplifier AMP2 outputs a voltage to the control section 600 as the signal SS_(esc), the voltage being obtained by amplifying the voltage of the input signal SW_(esc) at a predetermined amplification factor (e.g., 10³ times).

The control section 600 detects the amount of soot S contained in the exhaust gas through use of the signal SW_(esc) (low sensitivity signal) and the signal SS_(esc) (high sensitivity signal) input from the ion current measurement circuit 740. No particular limitation is imposed on the method of detecting the amount of soot S contained in the exhaust gas from these signals representing the leakage current I_(esc). For example, in the case where the control section 600 stores a map or a relational expression showing the relation between the voltage of the signal and the amount of soot S contained in the exhaust gas, the control section 600 can calculate the amount of soot S contained in the exhaust gas by using the map or the relational expression.

The control section 600 of the present embodiment obtains each of the voltages, which are analog signals input thereto as the signals SS_(esc) and SW_(esc), as a digital value of a predetermined resolution (for example, 8 bits). Also, the control section 600 is configured such that the size of the voltage readable range (the range of the full scale) becomes the same for the signals SS_(esc) and SW_(esc) input thereto.

The signal SS_(esc) (high sensitivity signal) has a higher sensitivity (resolution) for the leakage current I_(esc) as compared with the signal SW_(esc) (low sensitivity signal). For example, whereas a voltage level of the signal SW_(esc) of 1 V corresponds to a magnitude of the leakage current I_(esc) of 1 nA, a voltage level of the signal SS_(esc) of 1 V corresponds to a magnitude of the leakage current I_(esc) of 1 pA. Meanwhile, the control section 600 has the same voltage resolution (the minimum recognizable potential difference) (for example, 0.02 V) for both the signals SS_(esc) and SW_(esc). Accordingly, the magnitude of the leakage current I_(esc) corresponding to the voltage resolution of the control section 600 is small for the case of the signal SS_(esc) (e.g., 0.02 pA) and is large for the case of the signal SW_(esc) (e.g., 0.02 nA). In other words, the control section 600 can detect a smaller change in the leakage current I_(esc) from signal SS_(esc), as compared with the signal SW_(esc).

Therefore, the amount of soot S contained in the exhaust gas obtained from the signal SS_(esc) is smaller in the minimum recognizable unit and is higher in accuracy than the amount of soot S contained in the exhaust gas obtained from the signal SW_(esc). Meanwhile, the readable voltage range (e.g., 0 to 5 V) of the control section 600 is set to cover the entire voltage range of the signal SW_(esc). Therefore, a range in which the amount of soot S contained in the exhaust gas can be measured through use of the signal SW_(esc) is wider than a range in which the amount of soot S contained in the exhaust gas can be measured through use of the signal SS_(esc). If the amount of soot S contained in the exhaust gas falls within a range corresponding to the entire voltage range of the signal SW_(esc), the amount of soot S can be measured within the entire range.

As can be understood from the above, when the voltage of the signal SS_(esc) falls within the readable voltage range, the control section 600 can accurately measure the amount of soot S contained in the exhaust gas through use of the signal SS_(esc), and when the voltage of the signal SS_(esc) falls outside the readable voltage range, the control section 600 can measure the amount of soot S contained in the exhaust gas through use of the signal SW_(esc) which allows measurement within a wider range.

1-5. Corona Current Measurement Circuit

FIG. 5 is an explanatory view schematically exemplifying the configuration of the corona current measurement circuit 730. The corona current measurement circuit 730 is constituted as a so-called optical-coupling-type isolation amplifier whose input and output sides are isolated from each other. The input side of the corona current measurement circuit 730 belongs to the secondary side of the electric circuit section 700 (FIG. 3), and the output side of the corona current measurement circuit 730 belongs to the primary side of the electric circuit section 700. The corona current measurement circuit 730 includes a secondary-side operational amplifier 731, an A/D converter 732, a light emitting section 733, a light receiving section 734, a primary-side operational amplifier 735, and a D/A converter 736.

The two input terminals of the secondary-side operational amplifier 731 are connected to the wiring line 761 and the wiring line 762, respectively, and the output terminal thereof is connected to the A/D converter 732. The secondary-side operational amplifier 731 amplifies the potential difference between the wiring line 761 and the wiring line 762 and outputs the amplified potential difference to the A/D converter 732. The potential difference between the wiring line 761 and the wiring line 762 is the potential difference between the opposite ends of the shunt resistor 230 (FIG. 3) whose resistance is known, and correlates with the current flowing through the signal line 223 (FIG. 3) (the secondary-side current (I_(dc)+I_(trp)+I_(c))). Namely, the secondary-side operational amplifier 731 amplifies an analogue voltage signal representing the magnitude of the current flowing through the signal line 223 (FIG. 3) and outputs the amplified analogue voltage signal to the A/D converter 732.

The A/D converter 732, which is connected to the secondary-side operational amplifier 731 and the light emitting section 733, converts the analog signal output from the secondary-side operational amplifier 731 to a digital signal and outputs the digital signal to the light emitting section 733.

The light emitting section 733 includes an LED and is connected to the A/D converter 732 and the secondary-side ground SGL. The light emitting section 733 converts the digital voltage signal output from the A/D converter 732 to an optical signal.

The light receiving section 734 includes a photodiode and is connected to the primary-side operational amplifier 735 and the primary-side ground PGL. The light receiving section 734 converts the optical signal output from the light emitting section 733 to a current signal and outputs the current signal to the primary-side operational amplifier 735. In this manner, the light emitting section 733 and the light receiving section 734 are electrically and physically isolated from each other, and signals are transmitted between the light emitting section 733 and the light receiving section 734 through the mediation of light.

The primary-side operational amplifier 735 is connected to the light receiving section 734 and the D/A converter 736, and forms a current-voltage-conversion circuit. The primary-side operational amplifier 735 convers the current signal output from the light receiving section 734 to a voltage signal and outputs the voltage signal to the D/A converter 736. The D/A converter 736, which is connected to the primary-side operational amplifier 735 and the wiring line 763, converts the digital signal output from the primary-side operational amplifier 735 to an analog signal and outputs the analog signal to the control section 600 (FIG. 3) through the wiring line 763. Since the corona current measurement circuit 730 has the above-described configuration, the corona current measurement circuit 730 can output to the primary-side control section 600 the signal input from the secondary-side signal line 223, while maintaining the isolation between the primary side and the secondary side.

1-6. Auxiliary Electrode Current Measurement Circuit

FIG. 6 is an explanatory view schematically exemplifying the configuration of the auxiliary electrode current measurement circuit 780. The auxiliary electrode current measurement circuit 780 includes a resistor 784, an operational amplifier 785, a transistor Tr1, and a resistor 786.

One input terminal of the operational amplifier 785 is connected to the second wiring line 222 at a position between the short protection resistor 754 and the second electrode 132. The other input terminal of the operational amplifier 785 is connected to the emitter of a transistor Tr1 and is connected, through the resistor 784, to the second wiring line 222 at a position between the short protection resistor 754 and the second rectification circuit 752. The output terminal of the operational amplifier 785 is connected to the base of the transistor Tr1. The transistor Tr1 is a PNP-type transistor, and its collector is connected to the secondary-side ground SGL through the resistor 786.

The connection point between the collector of the transistor Tr1 and the resistor 786 is connected to the control section 600. Namely, the auxiliary electrode current measurement circuit 780 is configured to output to the control section 600 an auxiliary electrode current signal S_(ir) which represents the voltage V_(R3) between the opposite ends of the resistor 786. Notably, since the voltage V_(R3) between the opposite ends of the resistor 786 changes with the auxiliary electrode current I_(ir), the auxiliary electrode current signal S_(ir) can be utilized as a signal representing the auxiliary electrode current I_(ir).

When the particulate sensor 100 is operating normally, although a voltage is applied from the second rectification circuit 752 to the second electrode 132 through the second wiring line 222, no current flows to the second wiring line 222 because the second electrode 132 and the casing CS are electrically insulated from each other. However, for example, in the case where soot or the like lowers the insulation resistance between the second electrode 132 and the casing CS to thereby form a short circuit therebetween, the auxiliary electrode current I_(ir) flows between the second electrode 132 and the casing CS, and the auxiliary electrode current I_(ir) flows to the second wiring line 222.

The magnitude of the auxiliary electrode current I_(ir) can be calculated by the following expression (2). _(ir) =V _(R3) ×R2/{(R1×R3)×(1−1/h _(FE))}  (2)

In this expression, V_(R3) is the voltage between the opposite ends of the resistor 786, h_(FE) is the DC current amplification factor of the transistor Tr1, R1 is the resistance of the short protection resistor 754, R2 is the resistance of the resistor 784, and R3 is the resistance of the resistor 786. Of these values, the DC current amplification factor h_(FE) is a known value determined by the characteristics of the transistor Tr1, and the resistances R1, R2, and R3 are known values determined by the characteristics of the short protection resistor 754, resistor 784, and the resistor 786, respectively.

As described above, the control section 600 can detect the voltage V_(R3) between the opposite ends of the resistor 786 (hereinafter referred to as the “end-to-end voltage V_(R3)”) based on the auxiliary electrode current signal S_(ir) received from the auxiliary electrode current measurement circuit 780. Therefore, the control section 600 can compute the magnitude of the auxiliary electrode current I_(ir) through use of the end-to-end voltage V_(R3) and the expression (2) by storing the expression (2) in advance.

1-7. Processing of Control Section 600

The microcomputer of the control section 600 executes sensor state determination processing. FIG. 7 is a flowchart showing the sensor state determination processing. The microcomputer starts this sensor state determination processing immediately after the particulate sensor 100 being so that it becomes possible to detect the amount of particulates.

In this sensor state determination processing, in S10, the microcomputer of the control section 600 first calculates the magnitude of the auxiliary electrode current I_(ir) (hereinafter referred to as the “auxiliary electrode current value”) using the end-to-end voltage V_(R3) and the expression (2). Subsequently, in S12, the microcomputer determines whether or not the auxiliary electrode current value calculated in S10 is equal to or greater than a GND short judgment value which is set in advance and shows that the second wiring line 222 is shorted to the secondary-side ground SGL. Notably, the GND short determination value is set to a very large value as compared with a cleaning judgment value which will be described below. In the case where the auxiliary electrode current value is less than the GND short judgment value (S12: NO), the microcomputer proceeds to S20. Meanwhile, in the case where the auxiliary electrode current value is equal to or greater than the GND short judgment value (S12: YES), in S14, the microcomputer displays a GND short annunciating image on the display section 920, the GND short annunciating image showing that the second wiring line 222 is shorted to the secondary-side ground SGL. The microcomputer then stops the control of the particulate sensor 100 and ends the sensor state determination processing.

In S20, the microcomputer determines whether or not the auxiliary electrode current value calculated in S10 is equal to or greater than a cleaning judgment value (for example, 100 μA in the present embodiment) which is set in advance and shows that the particulate sensor 100 must be cleaned. In the case where the auxiliary electrode current value is less than the cleaning judgment value (S20: NO), in S30, the microcomputer resets (sets to 0) an annunciation counter provided in the RAM of the microcomputer. Subsequently, the microcomputer proceeds to S10.

Meanwhile, in the case where the auxiliary electrode current value is equal to or greater than the cleaning judgment value (S20: YES), in S40, the microcomputer increments (adds one to) the annunciation counter. Subsequently, in S50, the microcomputer determines whether or not the value of the annunciation counter is equal to or greater than an annunciation judgment value (a value corresponding to, for example, 10 sec in the present embodiment) set in advance.

In the case where the value of the annunciation counter is less than the annunciation judgment value (S50: NO), the microcomputer proceeds to S10. Meanwhile, in the case where the value of the annunciation counter is equal to or greater than the annunciation judgment value (S50: YES), in S60, the microcomputer displays a cleaning prompting image on the display section 920, the cleaning prompting image prompting cleaning of the particulate sensor 100. The microcomputer then stops the control of the particulate sensor 100 and ends the sensor state determination processing.

The particulate measurement apparatus 300 configured as described above controls the particulate sensor 100 which includes the ion generation section 110, the exhaust gas electrification section 120, the ion trapping section 130, and the second electrode 132 and which measures the amount of particulates.

The ion generation section 110 generates ions by means of corona discharge. The exhaust gas electrification section 120 electrifies at least a portion of particulates contained in a gas under measurement by using the ions. The ion trapping section 130 traps at least a portion of the ions generated by the ion generation section 110 but not used for electrifying the particulates. The second electrode 132 is maintained at a potential which repulses the ions and assists in the trapping of the ions at the ion trapping section 130.

The particulate measurement apparatus 300 includes the second isolation transformer 720 b and the auxiliary electrode current measurement circuit 780. The second isolation transformer 720 b applies a voltage to the second electrode 132 through the second wiring line 222, the voltage assisting the trapping of the ions at the ion trapping section 130. The auxiliary electrode current measurement circuit 780 detects the auxiliary electrode current I_(ir) flowing to the second wiring line 222.

The particulate measurement apparatus 300 determines the state of the particulate sensor 100 and the state of the second wiring line 222 based on the auxiliary electrode current I_(ir) detected by the auxiliary electrode current measurement circuit 780 (S10, S12, S20 to S50).

As described above, the particulate measurement apparatus 300 can determine that the particulate sensor 100 and/or the second wiring line 222 is in a state which is not normal by detecting the auxiliary electrode current I_(ir) which does not flow when the particulate sensor 100 is operating normally.

In a state in which the auxiliary electrode current I_(ir) flows, the measurement performance of the particulate sensor 100 may be lowered. In contrast, since the particulate measurement apparatus 300 can determine the state in which the auxiliary electrode current I_(ir) is flowing, the particulate measurement apparatus 300 can prevent the particulate sensor 100 from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current I_(ir). Thus, the particulate measurement apparatus 300 can suppress a lowering of the measurement performance of the particulate sensor 100.

Also, the particulate measurement apparatus 300 determines the state of the particulate sensor 100 by comparing the auxiliary electrode current value with the cleaning judgment value previously set based on the relation between the state of the particulate sensor 100 and the auxiliary electrode current value (S20).

As described above, the particulate measurement apparatus 300 can determine the state of the particulate sensor 100 by a simple method of comparing the auxiliary electrode current value and the cleaning judgment value. Therefore, the processing load of the particulate measurement apparatus 300 can be reduced.

Also, when the state in which the auxiliary electrode current value is equal to or greater than the cleaning judgment value continues for a time corresponding to the annunciation judgment value, the particulate measurement apparatus 300 displays the cleaning prompting image. This prompts the user to clean the particulate sensor 100, so as to suppress a lowering of the measurement performance of the particulate sensor (S60). Also, in the case where the auxiliary electrode current value is equal to or greater than the GND short judgment value, the particulate measurement apparatus 300 displays the GND short annunciating image (S14). Therefore, the particulate measurement apparatus 300 can prevent the particulate sensor 100 from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current I_(ir). Thus, the particulate measurement apparatus 300 can suppress a lowering of the measurement performance of the particulate sensor 100.

In the above-described embodiment, the exhaust gas electrification section 120 corresponds to the electrification chamber of the present invention; the ion trapping section 130 corresponds to the trapping section of the present invention; the second electrode 132 corresponds to the auxiliary electrode section of the present invention; the second isolation transformer 720 b corresponds to the voltage application section of the present invention; and the processing of S10, S12, and S20 to S50 corresponds to the state determination section of the present invention.

Also, the second wiring line 222 corresponds to the voltage application path of the present invention; the cleaning judgment value corresponds to the state judgement value of the present invention; and the processing of S60 and S14 corresponds to the suppression processing execution section of the present invention.

2. Second Embodiment

The particulate measurement system 10 of a second embodiment differs from that of the first embodiment in that the sensor state determination processing is modified.

FIG. 8 is a flowchart showing the sensor state determination processing of the second embodiment. The microcomputer starts this sensor state determination processing immediately after the particulate sensor 100 begins operating so that it becomes possible to detect the amount of particulates.

In this sensor state determination processing, in S210, the microcomputer of the control section 600 first calculates the auxiliary electrode current value in the same manner as in S 10 of the first embodiment. Subsequently, in S220, the microcomputer determines whether or not the auxiliary electrode current value calculated in S210 is equal to or greater than a small amount adhesion judgement value set in advance corresponding to an auxiliary electrode current value at the time when the amount of particulates having adhered to the interior of the particulate sensor 100 is a previously set small adhesion amount.

In the case where the auxiliary electrode current value is less than the small amount adhesion judgement value (S220: NO), in S230, the microcomputer resets a small amount adhesion counter, an intermediate amount adhesion counter, and a large amount adhesion counter which are stored in the RAM of the microcomputer. Subsequently, the microcomputer proceeds to S210.

Meanwhile, in the case where the auxiliary electrode current value is equal to or greater than the small amount adhesion judgement value (S220: YES), in S240, the microcomputer determines whether or not the auxiliary electrode current value calculated in S210 is equal to or greater than an intermediate amount adhesion judgement value set in advance. This intermediate amount adhesion judgement value is larger than the small amount adhesion judgement value and corresponds to an auxiliary electrode current value at the time when the amount of particulates having adhered to the interior of the particulate sensor 100 is a previously set intermediate adhesion amount.

In the case where the auxiliary electrode current value is less than the intermediate amount adhesion judgement value (S240: NO), in S250, the microcomputer increments the small amount adhesion counter. Subsequently, in S260, the microcomputer determines whether or not the value of the small amount adhesion counter is equal to or greater than an annunciation judgment value set in advance. In the case where the value of the small amount adhesion counter is less than the annunciation judgment value (S260: NO), the microcomputer proceeds to S210. Meanwhile, in the case where the value of the small amount adhesion counter is equal to or greater than the annunciation judgment value (S260: YES), in S270, the microcomputer displays on the display section 920 a small amount adhesion annunciating image informing that a small amount of particulates have adhered to the interior of the particulate sensor 100. After that, the microcomputer proceeds to S210.

In the case where the microcomputer determines in S240 that the auxiliary electrode current value is equal to or greater than the intermediate amount adhesion judgement value (S240: YES), in S280, the microcomputer determines whether or not the auxiliary electrode current value calculated in S210 is equal to or greater than a large amount adhesion judgement value set in advance. This large amount adhesion judgement value is larger than the intermediate amount adhesion judgement value and corresponds to an auxiliary electrode current value at the time when the amount of particulates having adhered to the interior of the particulate sensor 100 is a previously set large adhesion amount.

In the case where the auxiliary electrode current value is less than the large amount adhesion judgement value (S280: NO), in S290, the microcomputer increments the intermediate amount adhesion counter. Subsequently, in S300, the microcomputer determines whether or not the value of the intermediate amount adhesion counter is equal to or greater than the annunciation judgment value set in advance. In the case where the value of the intermediate amount adhesion counter is less than the annunciation judgment value (S300: NO), the microcomputer proceeds to S210. Meanwhile, in the case where the value of the intermediate amount adhesion counter is equal to or greater than the annunciation judgment value (S300: YES), in S310, the microcomputer displays on the display section 920 an intermediate amount adhesion annunciating image informing that an intermediate amount of particulates have adhered to the interior of the particulate sensor 100. After that, the microcomputer proceeds to S210.

In the case where the microcomputer determines in S280 that the auxiliary electrode current value is equal to or greater than the large amount adhesion judgement value (S280: YES), in S320, the microcomputer increments the large amount adhesion counter. Subsequently, in S330, the microcomputer determines whether or not the value of the large amount adhesion counter is equal to or greater than the annunciation judgment value set in advance. In the case where the value of the large amount adhesion counter is less than the annunciation judgment value (S330: NO), the microcomputer proceeds to S210. Meanwhile, in the case where the value of the large amount adhesion counter is equal to or greater than the annunciation judgment value (S330: YES), in S340, the microcomputer displays on the display section 920 a large amount adhesion annunciating image informing that a large amount of particulates have adhered to the interior of the particulate sensor 100. After that, the microcomputer proceeds to S210.

The particulate measurement apparatus 300 configured as described above determines the state of the particulate sensor 100 based on the auxiliary electrode current I_(ir) detected by the auxiliary electrode current measurement circuit 780 (S210 to S260, S280 to S300, and S320 to S330).

As described above, the particulate measurement apparatus 300 can determine that the particulate sensor 100 is in a state which is not normal by detecting the auxiliary electrode current I_(ir) which does not flow when the particulate sensor 100 operates normally. Therefore, the particulate measurement apparatus 300 can prevent the particulate sensor 100 from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current I_(ir). Thus, the particulate measurement apparatus 300 can suppress a lowering of the measurement performance of the particulate sensor 100.

Also, in the particulate measurement apparatus 300, the small amount adhesion judgement value, the intermediate amount adhesion judgement value, and the large amount adhesion judgement value are set as a plurality of state judgement values. The particulate measurement apparatus 300 determines, as states of the particulate sensor, states which are set in advance to differ from one another and correspond to the plurality of state judgement values, based on the results of a comparison between the auxiliary electrode current value and the small amount adhesion judgement value, the intermediate amount adhesion judgement value, and the large amount adhesion judgement value.

Thus, the particulate measurement apparatus 300 can determine a plurality of states of the particulate sensor 100 which differ from one another based on the auxiliary electrode current value. Therefore, the particulate measurement apparatus 300 can properly perform the processing of suppressing a lowering of the measurement performance of the particulate sensor 100 in accordance with the auxiliary electrode current value. For example, the cleaning time of the particulate sensor 100 is preferably increased in the order of the small amount adhesion annunciating image, the intermediate amount adhesion annunciating image, and the large amount adhesion annunciating image.

In the above-described embodiment, the processing of S210 to S260, S280 to S300, and S320 to S330 corresponds to the state determination section of the present invention; the small amount adhesion judgement value, the intermediate amount adhesion judgement value, and the large amount adhesion judgement value correspond to the state judgement values of the present invention; and the processing of S270, S310, and S340 correspond to the suppression processing execution section of the present invention.

3. Third Embodiment

The particulate measurement system 10 of a third embodiment differs from that of the first embodiment in that the particulate sensor 100 and the electric circuit section 700 have changed configurations, and particulate removal processing is executed in place of the sensor state determination processing.

FIG. 9 is a block diagram schematically exemplifying the configuration of the electric circuit section 700 of the third embodiment. The particulate sensor 100 of the third embodiment has an auxiliary electrode heating section 140. The auxiliary electrode heating section 140 includes an insulating pipe covering the circumference of the second electrode 132, and a heater embedded in the insulating pipe.

The electric circuit section 700 of the third embodiment includes a heater energization circuit 790. The heater energization circuit 790 is a circuit for supplying electric current to the heater of the auxiliary electrode heating section 140 by PWM (pulse-width-modulation) control to thereby heat the auxiliary electrode heating section 140. The heater energization circuit 790 is connected to one end of the heater through a heater wiring line 791 and is connected to the other end of the heater through a heater wiring line 792.

The microcomputer of the control section 600 of the third embodiment executes the particulate removal processing. FIG. 10 is a flowchart showing the particulate removal processing. The microcomputer starts this particulate removal processing immediately after the particulate sensor 100 begins operating so as to become possible to detect the amount of particulates.

In this particulate removal processing, in S510, the microcomputer of the control section 600 first calculates the auxiliary electrode current value in the same manner as in S10 of the first embodiment. Subsequently, in S520, the microcomputer determines whether or not the auxiliary electrode current value calculated in S510 is equal to or greater than a removal judgement value set in advance (for example, 100 μA in the present embodiment) which shows that particulate removal is required and which is set in advance. In the case where the auxiliary electrode current value is less than the removal judgement value (S520: NO), in S530, the microcomputer resets an energization counter provided in the RAM of the microcomputer. Subsequently, the microcomputer proceeds to S510.

Meanwhile, in the case where the auxiliary electrode current value is equal to or greater than the removal judgement value (S520: YES), in S540, the microcomputer increments (adds one to) the energization counter. Subsequently, in S550, the microcomputer determines whether or not the value of the energization counter is equal to or greater than a start judgment value (a value corresponding to, for example, 10 sec in the present embodiment) set in advance.

In the case where the value of the energization counter is less than the start judgment value (S550: NO), the microcomputer proceeds to S510. Meanwhile, in the case where the value of the energization counter is equal to or greater than the start judgment value (S550: YES), in S560, the microcomputer continuously supplies electricity to the heater of the auxiliary electrode heating section 140 through the heater energization circuit 790 for a removal energization period time set in advance. Subsequently, the microcomputer proceeds to S510.

The particulate measurement apparatus 300 configured as described above determines the state of the particulate sensor 100 based on the auxiliary electrode current I_(ir) detected by the auxiliary electrode current measurement circuit 780 (S510 to S550). As described above, the particulate measurement apparatus 300 can determine that the particulate sensor 100 is in a state which is not normal by detecting the auxiliary electrode current I_(ir) which does not flow when the particulate sensor 100 operates normally. Therefore, the particulate measurement apparatus 300 can prevent the particulate sensor 100 from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current I_(ir). Thus, the particulate measurement apparatus 300 can suppress a lowering of the measurement performance of the particulate sensor 100.

Also, when a state in which the auxiliary electrode current value is equal to or greater than the removal judgment value continues for a time corresponding to the start judgement value, the particulate measurement apparatus 300 supplies electric current to the heater of the auxiliary electrode heating section 140 so as to prevent the lowering of the measurement performance of the particulate sensor 100 (S560). Thus, the particulate measurement apparatus 300 can remove the particulates that have adhered to the vicinity of the second electrode 132 to thereby return the particular sensor 100 to a state in which the auxiliary electrode current I_(ir) does not flow. Therefore, the particulate measurement apparatus 300 can prevent the particulate sensor 100 from being continuously used in a state in which its measurement performance has been lowered due to the flow of the auxiliary electrode current I_(ir). Thus, the particulate measurement apparatus 300 can suppress a lowering of the measurement performance of the particulate sensor 100.

In the above-described embodiment, the processing of S510 to S550 corresponds to the state determination section of the present invention; the removal judgement value corresponds to the state judgement value of the present invention; and the processing of S560 corresponds to the suppression processing execution section of the present invention.

4. Other Embodiments

Embodiments of the present invention have been described; however, the present invention is not limited to the above-described embodiments and can be implemented in various forms without departing from the spirit and scope of the invention.

For example, in the above-described second embodiment, an image representing the amount of particulates having adhered to the interior of the particulate sensor 100 is displayed based on the results of comparison between the auxiliary electrode current value and the small amount adhesion judgement value, the intermediate amount adhesion judgement value, and the large amount adhesion judgement value. However, in the case where electric current can be supplied to the heater of the auxiliary electrode heating section 140 as in the case of the above-described third embodiment, the period of time during which electric current is supplied to the heater may be increased with the amount of particulates that have adhered to the interior of the particulate sensor 100, based on the results of comparison between the auxiliary electrode current value and the small amount adhesion judgement value, the intermediate amount adhesion judgement value, and the large amount adhesion judgement value.

In the above-described embodiments, the state of the particulate sensor 100 is notified to a user of the particulate measurement apparatus 300 by displaying an image. However, the method of annunciating the state of the particulate sensor 100 is not limited thereto. For example, a character string may be displayed, a lamp may be turned on or blinked, or a sound may be output.

The invention has been described in detail with reference to the above embodiments. However, the invention should not be construed as being limited thereto. It should further be apparent to those skilled in the art that various changes in form and detail of the invention as shown and described above may be made. It is intended that such changes be included within the spirit and scope of the claims appended hereto.

This application is based on Japanese Patent Application No. 2015-210884 filed Oct. 27, 2015 and Japanese Patent Application No. 2016-079720 filed Apr. 12, 2016. The above-identified applications are incorporated herein by reference in their entirety. 

What is claimed is:
 1. A particulate measurement apparatus for controlling a particulate sensor which measures the amount of particulates contained in a gas under measurement and which comprises an ion generation section for generating ions by means of corona discharge, an electrification chamber for electrifying at least a portion of the particulates contained in the gas under measurement using the ions generated in the ion generation section, a trapping section for trapping at least a portion of the ions generated by the ion generation section but not used for electrifying the particulates, and an auxiliary electrode section including an auxiliary electrode maintained at a potential which repulses the unused ions and which assists in the trapping of the unused ions at the trapping section, the particulate measurement apparatus comprising: a voltage application section which applies a voltage to the auxiliary electrode through a voltage application path, the applied voltage assisting the trapping of the ions at the trapping section; a current detection section which detects an auxiliary electrode current flowing to the voltage application path; and a state determination section which determines at least one of a state of the particulate sensor and a state of the voltage application path based on the auxiliary electrode current detected by the current detection section.
 2. The particulate measurement apparatus as claimed in claim 1, wherein the state determination section determines the state of the particulate sensor by comparing a value of the auxiliary electrode current and a state judgment value set in advance based on a relation between the state of the particulate sensor and the auxiliary electrode current.
 3. The particulate measurement apparatus as claimed in claim 2, wherein the state determination section includes a plurality of state judgment values set in advance; and the state determination section determines, as the state of the particulate sensor, one of states set in advance to differ from one another and which correspond to the plurality of state judgment values, based on the results of comparison between the plurality of state judgment values and the auxiliary electrode current.
 4. The particulate measurement apparatus as claimed in claim 1, further comprising a suppression processing execution section which executes suppression processing for suppressing a lowering of measurement performance of the particulate sensor in accordance with the result of the determination by the state determination section.
 5. The particulate measurement apparatus as claimed in claim 4, wherein the suppression processing comprises processing of annunciating the result of the determination by the state determination section.
 6. The particulate measurement apparatus as claimed in claim 4, wherein the particulate sensor includes an auxiliary electrode heating section which is disposed around the auxiliary electrode section and which heats the auxiliary electrode section when the auxiliary electrode heating section is energized; and the suppression processing comprises processing of supplying electric current to the auxiliary electrode heating section.
 7. A particulate measurement system comprising: the particulate measurement apparatus as claimed in claim 1; and a particulate sensor connected to the particulate measurement apparatus. 